It was a fun action movie, with a brilliant cast (especially Jackman and Schreiber), a good plot and it was more down to the Earth than the last X-Men films. I liked the gritty style of it, and all the action scenes were cool (especially the tower fight).
I never read the comics though, which could probably explain why I enjoyed all 4 X-films so far.
It was more product than art or entertainment, created merely to retain rights on something and shoehorned, rather indelicately, a bunch of unnecessary characters in it, again, merely to retain rights. It was sloppily produced, such as showing locations we had already seen, but for some reason they looked completely different now. And "gritty?"
It was overly glossy in its presentation of its character (which is the opposite of how the character should be presented) and it's very quality was cheap. Cartoon claws, anyone? There were vast swaths of it that didn't even make sense on a character level. This guy comes into your kitchen with your radiator or sink or whatever cleanly cut in half and apologizes, and you just say put it over there and don't worry about it? It was cleanly cut in in half!?!
That didn't strike anyone as curious?
Just all around a lazy, lazy film. That's why people don't like it. Oh, and all the fights, especially the tower fight, were shot like shit.